1. Field of the Invention
The present invention relates to a color character indicating apparatus for use in a color display system operating with a composite video signal, and more specifically to an apparatus for inserting color character data into a composite video signal, used in a system such as a video tape recorder which does not use a so-called R.G.B signal.
2. Description of Related Art
A typical one of conventional character indicating apparatuses for use in a color display system operating with a composite video signal comprises a display controller receiving a horizontal synchronizing signal and a vertical synchronizing signal for generating a character generation timing signal and a character output timing signal. In response to the character generation timing signal, a character generator selectively activates a white output control signal and a black output control signal in accordance with character data generated within the character generator, so that a white potential level or black potential level is generated as an output character signal. This output character signal is outputted as an output composite video signal in place of an input composite video signal. Namely, the output character signal is inserted into the composite video signal. In this case, a displayed character is white or black in color which can be displayed with only a DC level.
In the case of a color character indication, the input composited composite video signal is converted into a digital signal by an A/D converter. On the other hand, a display controller receives a horizontal synchronizing signal and a vertical synchronizing signal and generates a character generation timing signal and a character output timing signal, and a character generator receiving the character generation timing signal generates a R (red) signal, a G(green) signal and a B (blue) signal in accordance with character data generated within the character generator. In a data mixer or data synthesis circuit, the digitized composite video signal is mixed with the R, G and B signals in response to the character output timing signal, and the synthesized digital signal is converted into an analog composite video signal by a D/A converter.
As known, a video data portion of a composite video signal is a synthesis signal composed of a luminance signal and a carrier chrominance signal, and a color is represented by a DC component level of the luminance signal, and a phase difference of the carrier chrominance signal from a color synchronization signal and an amplitude of the carrier chrominance signal.
In the first example of the above mentioned conventional character indicating apparatus, since the signal of only the DC level having no amplitude is inserted into the composite video signal, a character displayed on a screen is a black-and-white character. Accordingly, it is not possible to display a colored character.
The second example configured to be capable of indicating a colored character, has to include the A/D converter and the D/A converter, which ar required to be have a high degree of precision in order to prevent deterioration of quality of an image to be displayed. Therefore, it is inevitably expensive.